This invention relates to an assembly comprising first and second fasteners and a baulking element.
It is known to use grooved clamp couplings to secure high pressure and high temperature ducting in engine bleed systems. Grooved clamp couplings typically comprise a pair of hinged jaws which clamp about respective flanges at the ends of the parts to be clamped together. The jaws are secured together at their free ends by a fastener, such as a nut and bolt arrangement. The clamping force exerted by the jaws is controlled by tightening of the fastener. In safety critical applications it is often necessary to provide a redundant fastener which is arranged adjacent the primary fastener.
The coupling is fastened by tightening the redundant fastener and then the primary fastener. This ensures that the clamping force exerted by the jaws and the stress through the coupling and/or fasteners is controlled by tightening of the primary fastener and not the redundant fastener. Consequently, once the primary fastener has been tightened it is important to ensure that the redundant fastener is not tightened further.
Systems that prevent tightening of fasteners in an incorrect sequence are known. For example, it is known to dispose a baulking arm made from sheet metal below the nut of the primary nut and bolt arrangement. The baulking arm is rotatable about the shank of the bolt from a non-baulking position to a baulking position.
The redundant nut is first tightened using a socket wrench. The primary nut is then tightened to push down and rotate the baulking arm over the top of the redundant nut. The baulking arm prevents a socket wrench from being placed over the redundant nut thereby preventing the redundant nut from being tightened further. A coil spring is provided to urge the baulking arm away from the redundant nut so that the baulking arm moves away from the redundant nut when the primary nut is loosened to allow access to the redundant nut. The existing baulking arrangement is complex to manufacture and unreliable. Further, the baulking arm and the spring are easily, damaged or deformed.